The invention relates generally to synchronous reluctance machines and more specifically to, fault tolerant synchronous reluctance machines.
Electric machines such as alternating current (AC) machines are typically not inherently fault tolerant. One of the primary reasons is that windings of AC machines are closely coupled magnetically. Thus, a short circuit in one winding affects adjacent phases. In a permanent magnet AC machine, rotating magnets generate potentially dangerous high currents in a short circuit path. Hence, adjacent phases may be seriously affected.
On the other hand, an electric machine such as a synchronous reluctance machine does not have rotating magnets, which makes it significantly more fault-tolerant. The fault-tolerance of a synchronous reluctance machine can be further enhanced by using concentrated windings on projecting stator poles. In this case, the phase windings are devoid of magnetic coupling so that high currents in a winding do not magnetically induce high currents in adjacent phase windings. A pair of diametrically opposite pole windings on the stator is connected in series or parallel to form an independent phase winding of a multiphase synchronous reluctance machine. Motoring torque is produced by switching current in each phase winding in a predetermined sequence that is synchronized with angular position of the rotor such that a magnetic force of attraction results between the poles of the rotor and the stator that approach each other.
In a typical synchronous reluctance machine, the rotor includes a series of alternating channels of iron and air extending axially along an active length of the machine. The iron channels provide an easy path for eddy current generated by the windings on the stator poles to flow. Consequently, this may lead to an undesirable amount of eddy current loss.
Further, while the typical synchronous reluctance machine provides several advantages over conventional electric machines such as AC machines as discussed above, a significant amount of noise, torque-ripple, vibration and windage losses may occur at high operating speeds and high operating temperatures if not properly designed.
Hence, there is a need to design an improved synchronous reluctance machine that addresses the aforementioned issues.